Estimate the area between the graph of f(x) and the x-axis for 1 ≤ x ≤ 9 using four rectangles and the right hand endpoint for the height of each rectangle. Your answer should be a whole number.

The answer is 45. For some reason, I get 53. For delta x, I get 2. When I add everything up, I get 53. Could someone explain to me what I'm doing wrong here? Thanks.